As one of main raw materials of LED light bars, a white covering film has been widely applied. At present, the white covering film mainly has two manufacturing methods. The first method is to use a white polyimide film, coat a layer of adhesive on a surface of the white polyimide film and compound the white polyimide film with a release material. The other method is to use an ordinary yellow polyimide film, coat a layer of white ink on a surface of the ordinary yellow polyimide film, coat a layer of adhesive on another side of the yellow polyimide film and compound the yellow polyimide film with a release material.
However, since the price of the white polyimide film is very expensive, the white polyimide film is not often applied in a market. Most of users still select a method for coating a layer of white ink on the ordinary yellow polyimide film.
With the development of thinning of products, higher and higher requirements are also proposed for the thickness of the white covering film. The manufacturing method for the pure white polyimide film is difficult to satisfy this need currently because on one hand, the price is excessively expensive, and on the other hand, a covering property and other characteristics after the products become thinner are difficult to be realized simultaneously. However, the manufacturing method for coating a layer of white ink on the ordinary yellow polyimide film is also difficult to satisfy a thinning need because the thickness is difficult to be reduced due to existence of three layers such as a polyimide layer, an adhesive layer and a white ink layer in spite of low price.